To explore the relationship between alcohol induced osteonecrosis of the femoral head (ONFH) and the single nucleotide polymorphisms (SNP) of methylene tetrahydrofolate reductase (MTHFR) 677 C/T.From July 2005 to May 2008, eighty-nine male patients with alcohol induced ONFH were selected as the patient group, aged from 24 to 58 years old (mean 44.3 years old). The time of drinking was about 17 years, 375 mL/day. The imaging evidence showed ONFH with no other history associated to ONFH. Seventy-seven male healthy adults were selected as the control group, aged from 23 to 52 years old (mean 42.7 years old). The time of drinking was about 14 years, 335 mL/day. The imaging evidence showed no ONFH. The 2 mL blood sample was acquired from every subject. DNA was purified from leucocyte at first, then was implicated by PCR, the product of PCR was sequenced at last. The SNP of MTHFR 677 C/T was analyzed with SPSS 12.0 software package.The TT genotype and T allele frequencies of MTHFR 677 C/T were 27.2% and 52.0% (P > 0.05) in the control group, and the distribution of genotype was consistent with Hardy-Weinberg equilibrium. The genotype frequencies of CC, CT and TT were 23.4% (18 cases), 49.4% (38 cases) and 27.2% (21 cases) in the control group, were 14.6% (13 cases), 36.0% (32 cases) and 49.4% (44 cases) in the patient group; showing statistically significant differences (P < 0.05). The allele frequencies of C and T were 48.0% (74) and 52.0% (80) in the control group, and were 32.6% (58) and 67.4% (120) in the patient group; showing statistically significant differences (P < 0.05). The frequencies of C, T alleles and TT genotype were higher in the patient group than in the control group, showing statistically significant differences (P < 0.05). The odds ratios were 0.523, 1.914 and 2.607, respectively; the 95% confidence interval were 0.335-0.816, 1.226-2.987, 1.359-5.001, respectively.The relationship may exist between the SNP of MTHFR 677 C/T and alcohol induced ONFH.